1. Field of the Invention
This invention relates to coke ovens and more particularly to process and apparatus for removing carbon deposits from coke oven gas offtakes.
2. Description of the Prior Art
In the well known process for producing coke, coal is heated in a coke oven in the substantial absence of air, thereby breaking down the complex coal substance and causing to be evolved combustible gases together with condensible tars and oils leaving as residue, coke. While the precise composition of the gases and tar evolved varies widely depending on the temperature and type of coal employed, such evolved substances are valuable by-products which in the coke ovens (termed "by-product ovens") are removed from the exiting gases. Typically, a by-product oven is provided with one or more large gas offtakes which provide communication between the coke oven chamber and a collector main to provide for the transfer of the gases evolved in the oven to a processing plant for subsequent isolation and recovery of the components thereof. Coke ovens are built adjacent one another and form a coke oven battery which may contain as many as 24 to 48 or more coke ovens in a single battery. Some coke oven batteries are provided with a collector main at each end of the coke ovens which services all of the ovens in the battery.
As the generated gases pass over and through the bed of coal being heated in the oven, some particulate matter is picked up by the gases and carried to the gas offtakes where the particles come into contact with the hot walls and are softened and caused to adhere to these surfaces. In addition, coal tars and other thermal decomposition by-products of the coal are deposited and accumulate in the gas offtake passages, as well as on the inner surfaces of the roof and side walls of the oven. Gradually, the accumulations of carbon deposits build up in the gas offtake passages which can eventually be clogged by these accumulated deposits. If these passages were to close completely, the pressure in the coke oven would build up and the gases evolved therein would escape from the oven by blowing off the charging port covers which are located on the top of the ovens and/or by leaking around the oven doors, thereby presenting the very real danger of ignition of these heated gases, which would be hazardous to the operators of the ovens. Therefore, it is desirable to avoid excessive accumulations of carbon deposits in coke oven gas offtakes.
Conventionally, the ovens are cleaned beween coal charges to the ovens by methods which may involve scraping the interior gas offtake surfaces to dislodge the carbon deposits that have formed. However, such scraping methods inherently involve the use of force to remove these deposits, thus increasing the wear upon the refractory oven surfaces upon which these deposits have formed. Moreover, manual methods of scraping, as by ramming a steel rod into the gas offtake to dislodge the deposits, are somewhat harardous to the personnel involved and are so inefficient. On the other hand, mechanical methods of scraping necessitate added expense due to increased equipment and labor requirements. Furthermore, such scraping operations to remove carbon deposits may be safely performed only when the ovens are substantially empty.
Other methods, such as that disclosed in U.S. Pat. No. 1,862,028, which have been developed for removing carbon deposits involve supplying large quantities of air to the hot, empty oven in an effort to oxidize the carbon deposits, and thereby effectuate their removal. In such methods, a steam jet is typically employed to draw air downwardly through a gas offtake which has been previously opened to the atmosphere and dampered from the collecting main, thereby oxidizing the carbon deposits on the inner surfaces of the gas offtake. The oxidation products and steam then escape through the open charging ports in the coke oven roof. Subsequently, the direction of the steam jet is reversed and air is drawn into the oven through the open charging ports, passing across the inner surfaces of the oven roof to oxidize carbon deposits thereon and exiting the oven to the atmosphere via the gas offtake. However, such air decarbonizing methods are disadvantageous because they may only be performed when the oven is substantially empty to prevent the undesired oxidation of the coal and coke content of the oven bed itself. In addition, such air decarbonization steps may only be performed for a relatively short period of time since the very act of forcing air over the oven surfaces cools these surfaces and eventually lowers their temperature below that which is necessary to sustain the desired oxidation reaction. Thus, in most instances scraping methods are required to supplement the carbon deposit removal effectuated by air decarbonizing.
Accordingly, what is needed is a safer, easier, more efficient and thorough process and apparatus to clean the inner surfaces of coke oven gas offtakes.